Ablation rate constant

Ablation products attenuation coefficient (10 cm ) Ablation rate constant (ng.ns. MW. cm )... 

Ablation rate constant definition, 418 determination, 414,417f Ablative photodecomposition description, 411 See also Photoablation Ace ty la ted m-cresol—novolac copolymers, preparation, 193... 

Figure 3. Ablation parameters at 193 nm for various polymers a, rate constant k and b, screening coefficient fJ. See Table I for acronyms.

The photoablation behaviour of a number of polymers has been described with the aid of the moving interface model. The kinetics of ablation is characterized by the rate constant k and a laser beam attenuation by the desorbing products is quantified by the screening coefficient 6. The polymer structure strongly influences the ablation parameters and some general trends are inferred. The deposition rates and yields of the ablation products can also be precisely measured with the quartz crystal microbalance. The yields usually depend on fluence, wavelength, polymer structure and background pressure. 

More recently, Boley (B9) shows that the method can be extended to find minimum and maximum bounds for ablation rates. The proof is based on a uniqueness theorem deriving from a theorem due to Picone (P3) and leads to the physically obvious result that the higher the heat input rate, the higher the melting rate. The procedure consists of forming a lower bound for the known arbitrary heat input function in terms of a sequence of constant heat flux periods, for which, as noted above, the solution can be written in terms of integrals of the error function. Upper bounds are constructed in a similar manner. 

Fig. 10 Schematic of the laser intensity (I), temperature (T) distribution within the material. Thermal bond breaking (of the polymer) with the rate constant k(T) takes place within this volume, producing a distribution of broken bonds and plausibly of volatile species within the polymer matrix. The figure also illustrates the difference between the volume and surface models advanced for the theoretical description of ablation of polymers. The subscript s denotes the receding surface...

The ablation rate of PTFE at a constant fluence increases for irradiation between 193 and 308 nm and reaches a maximum value of 60 pm/pulse before it starts decreasing with longer wavelengths [99]. The ablation process could also be explained by applying simple photothermal or photochemical models. 

The cathode is continuously rotated by means of an external motor in order to allow constant ablation conditions for all pulses and a homogeneous consumption of the rod. Higher deposition rates can be obtained by substituting the simple cylindrical nozzle with a more complex one (called focuser) as described in Reference 28. Exploiting inertial aerodynamic effects [28,29], the focuser reduces the angular semiaperture of the beam from 12° to less than 1° concentrating the cluster on the center of the beam. 

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